The Somali expatriate community in Britain provides a sizeable market for imports of khat, according to this BBC story:

Around seven tonnes of khat leaves, which is an evergreen shrub which grows in mountainous areas across Africa, is estimated to be imported into the UK each week from Ethiopia, Yemen and Kenya.

Khat is legal in Britain, though illegal in the US and Canada. Here's a summary of the effects of khat consumption, taken from the linked BBC article:

EFFECTS OF KHAT USEIt is a stimulant, making the user more alert and talkativeIt is an appetite suppressorIf chewed over a few hours, it produces a state of calmA chemical found in khat could boost the power of men's spermLong-term use can bring on insomnia, heart problems and sexual problemsCan bring on anxiety and aggressionCan bring on irritability, anger or violenceExcessive chewing can lead to sore mouths and infectionsIt can bring on depressionIt is associated with mental health issues among users